Complex Geometry Composite Armor for Military Applications

ABSTRACT

The present invention utilizes a layered armor concept, combining engineered and naturally-occurring materials, to mitigate damage to a vehicle from explosively formed projectiles (EFPs), particularly those projectiles with impact velocities greater than 2.25 km/s, reducing the velocity of the impacting projectile to less than 1.5 km/s upon exiting the composite armor system. The composite armor system incorporates a structural framework that contains and constrains a geometrical structure of rigid rods with the void spaces between the rods filled with a particulate matrix material. Because the composite armor can incorporate naturally-occurring particulate matrix materials that are readily available, the armor can be transported with less bulk system weight, allowing for additional weight reduction in air or sea transport applications.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of the filing of U.S. Provisional Patent Application Ser. No. 60/938,712, entitled “Complex Geometry Composite Armor Concept”, filed on May 18, 2007, and the specification thereof are incorporated herein by reference.

STATEMENT OF GOVERNMENT INTEREST

The United States Government has rights in this invention pursuant to Department of Energy Contract No. DE-AC04-94AL85000 with Sandia Corporation.

BACKGROUND OF THE INVENTION

The present invention is related to lightweight, composite armor, and more particularly, to a lightweight, composite armor system that utilizes particulate materials dispersed in a structure or rigid rods.

Improved vehicular and facility armor are needed by battle and protective forces to defend against an evolving enemy that is acquiring weapons with capabilities beyond conventional blast and fragment behavior associated with Improvised Explosive Devices (IEDs). The borderline shear/hydrodynamic penetration threat of an explosively formed projectile (EFP), which travels at velocities of >2.25 km/s, has typically been defended against by large thicknesses of either a single high-density material or a multi-layer composite laminate (Chobham armor). Another option for protection is reactive armor (such as explosive reactive armor and non-explosive reactive armor) in which a counter-explosive reaction or other mechanism acts to break up the threat and/or to increase the effective thickness that the threat must penetrate. Unfortunately, both such defenses, because of their significant weight penalty, have been restricted to large, difficult to transport vehicles (such as the M1A1 Abrams tank) or stationary facilities. High mobility vehicles such as the military Humvee (HMMWV) are not able to carry effective armor against such a threat, and have been shown in recent regional conflicts to be highly vulnerable. The armor on most up-armored HMMWV's is laminated hardened steel plates that total approximately 1″ (25.4 mm) thickness. While this level of armor protection is a significant improvement over no armor or the improvised armor that was being used at the beginning of the Iraq war, it does not provide sufficient protection against new threats such as the EFP. Additionally, its added mass also introduces vehicle durability and performance issues due to the increased weight and the higher center of gravity of the vehicle.

One armor protection concept utilizes a physics-based materials system integration to defeat high velocity projectiles. High velocity projectiles are defined here as having velocities greater than 1.5 km/sec. This is an important threshold velocity as it typically defines the lower level velocity regime for hydrodynamic material behavior—that is impact pressures are well in excess of conventional material strength and the resulting material interaction is essentially liquid behavior.

Conventional armor systems utilize two distinct material properties to defeat high velocity penetrators. The first property is the property of mass. Typically, substantial amounts of material must be utilized to defeat the threat, unless the armor material has very high density, in which case the required thickness of material can be inversely changed (proportionally decreased) with density. Use of mass to stop high velocity threats is an acceptable solution for fixed assets, but is problematic for protecting mobile assets such as armored vehicles and personnel carriers which have finite weight capacities.

The second mitigating property utilized is that of dwell. Materials such as ceramics have this unique capability. Dwell is the property by which mitigating materials can effectively erode an incoming threat (penetrator) for some period of time with no armor system penetration increase. After the dwell time, the incoming penetrator penetrates the protective material like conventional material.

Use of a single material—particularly in mass-based systems—is an inefficient method for protecting against hydrodynamic threats such as EFPs. This is because the comparatively heavy hydrodynamic regime material is also utilized to fully stop the threat even when it has been slowed below the hydrodynamic regime where conventional high strength low weight materials could be effective. In essence additional hydrodynamic regime armor material is needed to completely defeat the threat resulting in a heavier system. Furthermore, mass-based systems tend to not break up the penetrator if the armor system does not completely stop the threat. Multi-layer systems have the advantage to dispersing the penetrator over an area larger than the original penetrator diameter, reducing the residual penetrator effectiveness after passing through the armor system.

Additionally, explosive reactive armor systems are also commonly utilized to protect against hydrodynamic regime threats—particularly conical shaped charges. These systems essentially represent a mass-based system whereby the armor material is driven toward the incoming threat by utilizing the energy of detonating explosive, with the explosive being initiated by the incoming threat. These systems are not useful for light armored vehicles (Humvees) and are also ineffective for threats such as EFPs that do not have the proper velocity and diameter combination to promptly initiate the explosive material.

There are several considerations concerning the development and use of protective armor materials and systems. One consideration is weight. Protective armor for heavy but mobile military equipment, such as tanks and large ships, is known. Such armor usually comprises a thick layer of alloy steel, which is intended to provide protection against heavy and explosive projectiles. However, reduction of weight of armor, even in heavy equipment, is an advantage since it reduces the strain on all the components of the vehicle. Furthermore, such armor is quite unsuitable for light vehicles such as automobiles, jeeps, light boats, or aircraft, whose performance is compromised by steel panels having a thickness of more than a few millimeters, since each millimeter of steel adds a weight factor of 7.8 kg/m².

Armor for light vehicles is expected to prevent penetration of projectiles of any type, even when impacting at a speed in the range of 700 to 1000 meters per second. However, due to weight constraints it is difficult to protect light vehicles from high caliber armor-piercing projectiles, e.g. of 12.7 and 14.5 mm, since the weight of standard armor to withstand such projectile is such as to impede the mobility and performance of such vehicles. Another type of projectile arises from explosive devices. The armor is expected to prevent penetration of a variety of materials at high speeds and over a relatively large surface area.

Another consideration is cost. Overly complex armor arrangements, particularly those depending entirely on synthetic fibers, can be responsible for a notable proportion of the total vehicle cost, and can make its manufacture prohibitive.

Another consideration in armor design is compactness. A thick armor panel, including air spaces between its various layers, increases the target profile of the vehicle. In the case of civilian retrofitted armored automobiles which are outfitted with internal armor, there is simply no room for a thick panel in most of the areas requiring protection.

Another consideration is the robustness of the armor in the normal operation of the vehicle. For example, ceramic plates used for personal and light vehicle armor have been found to be vulnerable to damage from mechanical impacts caused by rocks, falls, and other contact from everyday operation.

These considerations lead to the overall evaluation of the availability, robustness and overall effectiveness of the armor to be utilized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the layered armor system of the present invention.

FIG. 2 illustrates a unidirectional rod geometrical structure.

FIG. 3 illustrates a bi-directional rod geometrical structure.

FIG. 4 illustrates an unaligned rod geometrical structure with rods of circular cross-section.

FIG. 5 illustrates an unaligned rod geometrical structure with rods of a diamond cross-section.

FIG. 6 illustrates an unaligned rod geometrical structure with rods of square cross-section.

FIG. 7 illustrates an aligned rod geometrical structure with rods of square cross-section.

DETAILED DESCRIPTION OF THE INVENTION

The present invention utilizes a layered armor concept, combining engineered and naturally-occurring materials, to mitigate damage to a vehicle from explosively formed projectiles (EFPs), particularly those projectiles with impact velocities greater than 1.5 km/s, reducing the velocity of the impacting projectile to less than 1.5 km/s, and even less than 1.0 km/s, upon exiting the composite armor system. Thus, the system is designed to be an effective defense against projectiles in the hydrodynamic velocity regime. Additionally, the system is designed to be at least partially self-healing so that the system can survive multiple impacts or impact events. By self-healing, it is meant that the system, or a self-healing element of the system, can be impacted by a projectile and return, at least in part, to the pre-impact state. Thus, any void space created by an impact will be at least partially filled, with outside intervention, by the system element due to the material characteristics of the system element.

The composite armor system incorporates a structural framework that contains and constrains a geometrical structure of rigid rods with the void spaces between the rods filled with a particulate matrix material (see FIG. 1). The system combines the materials in ways that take advantage of their individual properties, including their hardness, dwell, shock impedance, and energy absorption properties. The geometry and arrangement of the armor elements are critical to the performance of the armor system, based on comparison with results for simple layered arrangements. Because the composite armor can incorporate naturally-occurring materials that are readily available, the armor can be transported without the bulk of system material weight, allowing for additional weight reduction in air or sea transport applications. In addition to the system's enhanced performance when compared with conventional metal armor systems, it also has a side benefit of reduced collateral damage (spalling) in applications where the armor system is defeated by threats larger that can be mitigated by the system. Spalling results in a shotgun effect on the interior of vehicles. This is commonly seen in armored vehicles exposed to EFP penetrations.

The composite armor system of the present invention uses a layered, passive, composite armor system in which macroscopic heterogeneity, combined with a specific arrangement of elements, leads to significant improvements in defense against EFP-type threats: either better protection at a given weight, or equivalent protection at lesser weight when compared with conventional Rolled Homogeneous Armor (RHA) armor systems. The improved performance is measured in terms of a reduction in the damage of a metal witness plate behind the composite armor system.

The composite armor system uses commercially available structural metallic or ceramic elements embedded in an efficient energy-absorbing medium (a particulate matrix material) constrained or contained by ductile and compliant materials. In addition to the combination of materials, the system employs a unique complex geometry that leads to synergistic improvements, in that the combined behavior is superior to that of the individual components, and superior to simple layered arrangements of the same materials.

Several fundamental physical properties are thought to contribute to the reduced penetration in the composite armor arrangement of the present invention. The primary method is to employ the phenomenon known as “dwell”, in which a high velocity object contacting a constrained high compressive strength material “splashes” against the surface, rather than penetrating. In this complex geometry, ceramic rods can be used to promote this, and further, to promote it in a manner that recursively splits the incoming threat. Thus, the concept armor reduces the velocity and areal density of the incoming projectile in stages. For the ceramic elements to effectively produce this “splitting”, they must be macroscopic in size, i.e., comparable in size to the threat projectile. Another phenomenon thought to enhance the performance of this complex geometry composite armor system is the refraction of stress waves at interfaces of variable acoustic impedance, akin to the refraction of light in a prism. The geometry of the ceramic/particulate matrix material interface and separation of the ceramic elements takes advantage of this to disperse the shock waves to prevent the production of the tensile stress state that ceramics are vulnerable to. After the projectile has been substantially slowed and dispersed by the sacrificial front layers, the final layers can stop and distribute over a wide area the remnant energy, preventing energy transfer to the interior of the vehicle (or other object) being protected.

The framework containing the rigid rod structure and the matrix fill material can be either rigid or non-rigid, with self-healing properties. The framework can be composed of polymer plastic materials, such as thermoplastic resins including Lexan™ (a polycarbonate resin thermoplastic material) and Surlyn™, a thermoplastic ionomer resin, or other rigid materials, such as metals (for example, steel, copper and aluminum).

The geometrical structure of rods contained within the framework can be varied in several ways. The rods themselves are rigid and can be made from ceramic materials such as alumina, silicon carbine, zirconia, metal nitrides and metal titanates, metal materials, including but not limited to aluminum, steel, copper, iron and alloys thereof and high-density rubber materials (such as from tires). The rods can be attached to the framework as well as attached to some or all of the other rods in the structure. FIG. 2 shows various contemplated geometrical arrangements of the rods oriented in an essentially unidirectional geometrical structure. The rods can be arranged in aligned rows, non-aligned rows or other non-organized patterns. FIG. 3 shows one embodiment where the rods are arranged in a bi-directional structure where some of the rods are oriented in one direction that is angled, shown approximately perpendicular in the embodiment of FIG. 3, to other rods; other angles of intersection can be used. The rods can have various cross-sectional shapes, including a circular cross-section (FIG. 4), a diamond cross-section (FIG. 5), a triangular cross-section, a rectangular or square cross-section (FIG. 6), or any other polygonal cross-section. The rods can be unaligned (FIG. 2) in two rows or more than two rows or the rods can be aligned, as shown in FIG. 7. The geometrical structure of rods can contain rods of homogeneous characteristics or a variety of rods with different characteristics, both from a geometrical and physical property perspective. The rods can have diameters ranging from 1/16 inches to 6 inches (1.59-152.4 mm). In one embodiment, the rods can be of varying materials, varying diameters and varying cross-sectional geometries for a given unidirectional or bi-directional geometric framework.

Dispersed within the geometrical structure of rods is a particulate material, preferably with self-healing properties. In one embodiment, the particulate material is one that is a geologically-based material indigenous to the area in which the armor is to be utilized, such as sand. Alternatively, the fill material can be a man-made material. Generally speaking, hydrodynamic response of isotropic and equal compressive/tensile strength materials (such as metals) is driven almost entirely by the density of the material—implying that compressive and/or tensile strength has little to do with target material response (for example, enhancements in compressive strength do not help defeat the penetrating threat) For these type of materials, it is the mass of the target material that drives target response—that is “denser” materials of a given thickness will be penetrated less by a given threat than less dense materials of the same thickness.

However, there are also materials that are anisotropic and have unequal compressive and tensile strength materials, where the previous relationship between mass and penetration no longer holds true. Geologic materials (and many man made materials) have this latter set of properties, and in this case compressive strength does in fact become an indicator of target material response—that is materials in this class with higher compressive strength tend to resist penetration more than materials with less compressive strength. Desirable materials for defeating hydrodynamic regime threats in this class become those with very high compressive strengths, and even better accompanying low densities and resulting lower weights. Sand is one such viable material.

For the matrix fill materials, desirable material properties include high compressive strength—not necessarily in a static sense but when confined and or loaded at high rates—this is why sand is effective—with a density of between approximately 2.2 g/cm³ and 3.1 g/cm³. Many varieties of sand, with a variety of strength to weight ratios and grain geometries, have a fairly good strength-to weight ratio when strained at rates typical of an armor system. Furthermore, its compressive strength does not degrade with subsequent hits/loadings. Alternate materials for the matrix fill include combinations of geologic-based and ceramic materials, and others that possess better compressive strength to weight ratios compared to sand and various geologic materials already considered. The relative volume of rigid rods to the fill matrix can be varied over a wide range and still prove effective. Besides the particulate matrix material between the rods, there can also be a layer of particulate matrix material above and below the geometrical rod structure. Tests have shown that the relative volume of the rods to the particulate matrix material can be as low as approximately 10% or as high as 75% or greater, depending upon the desired cost to weight to performance ratio.

A series of test were conducted to determine the relative performance of various armor design concepts against a standardized 512 gram EFP slug with an impact velocity of 2.7 km/sec. Two metrics were utilized to determine performance of the armor systems: deformation of a steel witness plate in contact on the rear side of the armor cross section, and exit velocity. The performance of each armor system was compared to an equal weight steel Rolled Homogeneous Armor (RHA) layer. In each case, the layered armor system of the present invention demonstrated substantial increase in performance (measured in their ability to mitigate the EFP slug). In all cases, thickness of the various layered armor concepts where chosen such that the system would not completely defeat the threat—this allowed for the relative measurement of performance described above.

It should also be noted that the rod systems ability to break up and disperse the incoming uniform slug is quite effective when used against threats where the armor system would still be overwhelmed by the EFP slug.

In addition, testing was performed against a semi-infinite layer of RHA to determine EFP penetration ability in a simple RHA armor system like those currently employed in Humvees and other up-armored vehicles.

EXAMPLE 1 Baseline Semi-Infinite RHA Test

The test was a ½ scale EFP (269 gm of C4 explosive), tested against 2″ (50.8 mm) (8¼″ (6.35 mm) sheets) RHA. The test results showed penetration through the first 3 inches (76.2 mm), significant denting in last sheet (>76.2 mm). This test allows for comparison of the layered armor systems on an areal density/performance basis

EXAMPLE 2 Using Unidirectional Ceramic Rods (Diamond Rod Orientation)

As in Example 1, the test was ½ scale EFP (269 gm of C4 explosive), using a relative volume ratio of bars to matrix material of 25%, with unidirectional bars and with a diamond orientation of ¼″ (6.35 mm) alumina bars in 2.5″ (63.5 mm) of sand and a 1″ (25.4 mm) (4¼″ (6.35 mm) sheets) RHA witness plate, using a Lexan™ framework material. The test results showed a 6 mm dent in the 1st ¼″ (6.35 mm) steel layer.

In this test, the areal density of the system was 0.35 g/cm³. With the 1″ RHA witness plate (that experienced 6 mm denting) in the first ¼″ (6.35 mm) of material, the areal density was 1 g/cm³. This same threat completely defeated 76.2 mm of RHA (Areal Density: 76.2 mm RHA=1.94 g/cm³) and also produced substantial denting in the final 25.4 mm of material (101.6 mm of RHA has an areal density of 2.58 g/cm³).

EXAMPLE 3 Using Bidirectional Ceramic Rods (Diamond Rod Orientation)

As in Examples 1 and 2, the test was ½ scale EFP (269 gm of C4 explosive), using a relative volume ratio of bars to matrix material of 25% in both directions of the bi-directional bars, with a diamond orientation of ¼″ (6.35 mm) alumina bars in 2.5″ (63.5 mm) of sand and a polymeric sheet framework material, with 25.4 mm (4¼″ (6.35 mm) sheets) RHA backing. The test results showed a 6 mm dent in the 1st steel layer. Again, when compared with the Baseline RHA tests in Example 1, the Ceramic/Sand Matrix had a lighter areal density of 0.43 g/cm³ and an overall density of 1.08 g/cm³ with the RHA witness plates in place.

EXAMPLE 4 Baseline RHA Test—Thickness Chosen to Approximate Average Areal Density of Layered Armor Concepts

The test was generally performed according to the parameters described in Example 1, with 16.5 mm RHA to determine the EFP exit velocity. Based on two tests, the exit velocity was 1500-1700 m/s, with a baseline areal density using 16.5 mm RHA 0.42 g/cm³.

EXAMPLE 5 Exit Velocity Determination Using Bidirectional Ceramic Rods (Diamond Rod Orientation) Bidirectional Ceramic Bar Test

The test was generally performed according to the parameters described in Example 3, with a ½ scale EFP (269 gm of C4 explosive), 25%125% bidirectional ceramic bars, a diamond orientation of ¼″ (6.35 mm) alumina bars in 2.5″ (63.5 mm) of sand and a polymeric sheet framework. Based on two tests, the exit velocity was 880-1000 m/s. When compared with the essentially equal areal density of the Ceramic/Sand Matrix (0.43 g/cm³), an approximate 50% reduction in exit velocity is observed and a 75% reduction in energy of the fragments.

EXAMPLE 6 Exit Velocity Determination Using Bi-Directional Steel Rods (Diamond Rod Orientation) Bidirectional Ceramic Bar Test

The test was generally performed according to the parameters described in Example 3, with a ½ scale EFP (269 gm of C4 explosive), 25%/25% bidirectional steel bars, a diamond orientation of ¼″ (6.35 mm) in 2.5″ (63.5 mm) of sand and a Lexan™ framework. The exit velocity was 1100 m/s. The area density of the steel bar/sand matrix was 0.43 g/cm³.

The steel bar cross-section was reduced to 4.76 mm to maintain an areal density of 0.43 g/cm³ for comparative purposes—in this case a modest increase in exit velocity was observed, although still substantially better than a conventional RHA system. The substantial cost savings of steel bar over ceramics could make this solution attractive in some applications.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. 

1. A composite armor system, comprising: a particulate matrix material dispersed between a geometrical structure of rigid rods, said particulate matrix material and geometrical structure of rigid rods constrained within a structural framework.
 2. The composite armor system of claim 1 wherein the system is capable of reducing the velocity of a projectile impacting one side of said system from greater than 2.25 km/s to a velocity of the projectile exiting the other side of the system of less than 1.5 km/s.
 3. The composite armor system of claim 1 wherein the system is capable of reducing the velocity of a projectile impacting one side of said system from greater than 1.5 km/s to a velocity of the projectile exiting the other side of the system of less than 1.5 km/s.
 4. The composite armor system of claim 1 wherein the system is capable of reducing the velocity of a projectile impacting one side of said system from greater than 1.5 km/s to a velocity of the projectile exiting the other side of the system of less than 1.0 km/s.
 5. The composite armor system of claim 1 wherein said particulate matrix material comprises a geologically-based material.
 6. The composite armor system of claim 5 wherein said particulate matrix material is sand.
 7. The composite armor system of claim 1 wherein said particulate matrix material has a density between 2.2 g/cm³ and 3.1 g/cm³.
 8. The composite armor system of claim 1 wherein said particulate matrix material comprises a man-made material.
 9. The composite armor system of claim 1 wherein said particulate matrix material is self healing.
 10. The composite armor system of claim 1 wherein said structural framework is non-rigid and self-healing.
 11. The composite armor system of claim 1 wherein said structural framework is comprised of a material selected from a polycarbonate resin thermoplastic material, a thermoplastic ionomer resin, steel, copper and aluminum.
 12. The composite armor system of claim 1 wherein rigid rods are comprised of a material selected from the group consisting of ceramic materials, high-density rubber, aluminum, steel, copper, iron and alloys thereof.
 13. The composite armor system of claim 12 wherein the ceramic materials are selected from the group consisting of alumina, silicon carbine, zirconia, metal nitrides and metal titanates.
 14. The composite armor system of claim 1 wherein said geometrical structure of rigid rods comprise an aligned geometry.
 15. The composite armor system of claim 1 wherein said geometrical structure of rigid rods comprise an unaligned geometry.
 16. The composite armor system of claim 1 wherein said geometrical structure of rigid rods comprise rods with a cross-section selected from the group consisting of a circle, a triangle, a diamond, a rectangle, and higher-order polygons.
 17. The composite armor system of claim 16 wherein said rigid rods have a diameter between 1.6 mm and 152.4 mm.
 18. The composite armor system of claim 1 wherein the volume of the rigid rods to the volume of the particulate matrix material is between 10% and 75%.
 19. The composite armor system of claim 1 wherein the combination of the particulate matrix material and the geometrical structure of rigid rods has a density between 0.4 g/cm³ and 1 g/cm³.
 20. A composite armor system, comprising: an arrangement of multiple rows or rigid rods within a sand material, said arrangement contained within a rigid structure with means for attaching said rigid structure to a vehicle. 